Field of the Invention
The present invention relates to sterilized packages and containers. In particular, the present invention relates to sterilized packaging containing a highly efficient formaldehyde releasing composition.
Description of Related Art
There is a wide array of medical devices that must be sterilized prior to their use. In the medical field it is common to have articles that can be re-sterilized or disposable articles that are only used one time but are provided to the user already sterilized. The art uses a wide variety of methods to sterilize or re-sterilize medical articles including, ethylene oxide, formaldehyde, low temperature steam-formaldehyde, gamma/e-beam irradiation, steam autoclave, dry heat, and the like.
While gaseous sterilization is very effective, the handling and long periods of time needed to diffuse and remove the sterilant gas from the chamber containing large pallets of heavy cardboard boxes/packages is a problem. Because of the long contact times and purge cycles required for gaseous sterilization, most gaseous sterilizations take place mainly in industrial settings where the requirement for expensive equipment is more cost effective and careful control can take place during the sterilization cycle by someone experienced in the sterilization process. Also, high energy irradiation methods require expensive radiation facilities and certified personnel skilled in the use of radiation isotopes for the purpose of sterilization of medical products. Plastic components of medical products are often embrittled or damaged by the destructive nature of the irradiation process. In the non-industrial setting, such as a hospital or physician's office, historically one of the most widely used methods for sterilization is the use of high temperature steam autoclaves. Unfortunately, the temperature of an autoclave is not conducive for use with many of today's plastics or other heat sensitive medical products which are commonplace in the medical environment of today. Accordingly, many medical offices throw away reusable medical devices because there are currently no techniques that are suitable for the non-industrial setting that are both cost effective and easy to use in small medical facilities.
Some twenty-five years ago an attempt to solve the problem was made in U.S. Pat. No. 4,050,576 to Williams et al. In that patent a sterilant package included a relatively thick piece of poly acetal (which contains oxymethylene groups and stabilizing groups) which had been irradiated to effect chain cleavage of the polymer without depolymerization. The package, upon subsequent heating, caused the poly acetal to slightly depolymerize which caused a release of trace amounts of formaldehyde gas. Unfortunately, the irradiation doses required to achieve sufficient gas release for sterilization using this method were so high that the insert became very brittle and difficult to manage as indicated by low film breaking angles in embrittlement tests.
During the prior art timeframe, thermoplastic polyoxymethylenes were only commercially available as extremely viscous melts (low melt flow rates between 0.3 to 5.0 g/10 min as determined by ASTM D1238E) that limited the thermoformability into simple geometries, such as films, slabs, and rods, which required prolonged crystallization times that caused even further embrittlement and degradation of the material. Relatively thin fibers are impossible to form with these low melt flow rate polymers since spin blown fibers require higher melt flows. Severe plastic embrittlement caused by the combination of thicker part limitations and higher irradiation doses required to achieve sufficient gas release resulted in the prior art never being adopted commercially.